The colon is section of the large bowel. This article also covers the rectum and cecum as both have a similar mucosa.
Technically, the rectum and cecum are not part of the colon. Thus, inflammation of the rectum should be proctitis and inflammation of the cecum should be cecitis.
- 1 Anatomy
- 2 Common clinical problems
- 3 Grossing
- 4 Common non-neoplastic disease
- 5 Inflammatory diseases
- 6 Infectious
- 7 Rectal pathology
- 8 Neoplastic disease
- 9 Other
- 9.1 Colonic pseudo-obstruction
- 9.2 Pseudomelanosis coli
- 9.3 Angiodysplasia
- 9.4 Drugs
- 9.5 Graft-versus host disease
- 9.6 Bowel transplant
- 9.7 Chronic constipation
- 10 See also
- 11 References
- The large bowel may be submitted with segment names or with the distance to the anal verge.
A conversion between named segments and distance - as per NCI of the United States:
|Named segment||Distance to anal verge (cm)|
Common clinical problems
Top three (in adults):
- Colitis (radiation, infectious, ischemic, IBD (UC >CD), iatrogenic (anticoagulants)).
- Diverticular disease.
Infectious colitis with bleeding - causes:
- Enterohemorrhagic Escherichia coli (EHEC) -- commonly 0157:H7.
- Campylobacter jejuni.
- Clostridium difficile.
Infectious colitis in the immunosuppressed:
- Cytomegalovirus (CMV).
Types of specimens
Introduction to colorectal surgery:
- Colonic resection - remove a piece of large bowel.
- Total colectomy - leaves rectum and anus.
- Subtotal colectomy - part of colon removed --or-- some of the rectum remains.
- Right hemicolectomy - right colon + distal ileum.
- Lower anterior resection (LAR) - proximal rectum +/- sigmoid (for proximal rectal malignancies).
- Abdominoperineal resection (APR) - anus + rectum - results in a permanent stoma (for distal rectal malignancies).
- Stoma - these are often done emergently and then get cut-out after the patient's condition has settled.
- Doughnuts (also donuts) from an end-to-end anastomosis stapler.
- Often accompany lower anterior resections.
Identifying the specimen
- Transverse colon - has omentum.
- Ascending colon - usu. comes with ileocecal valve and a bit of ileum.
- Descending colon - has a bare area.
- Rectum - has adventitia.
- Bowel is prep'ed by opening it along the antimesenteric side.
- Dimensions - length, circumference at both margins.
- Radial margin/circumferential margin - should be painted.
- Rectum starts/sigmoid ends @ place where serosa ends on the posterior aspect of the bowel.
- The proximal, anterior aspect of the rectum has serosa, i.e. it is not painted.
- Rectum starts/sigmoid ends @ place where serosa ends on the posterior aspect of the bowel.
- There are several definitions for the rectum.
- In a survey of surgeons:
- 67% defined it by an anatomical landmark
- 35% of all respondants considered the peritoneal reflection the proximal boundary of the rectum.
- 30% defined the proximal boundary as a distance from the anal verge.
Common non-neoplastic disease
Polyps are the bread & butter of GI pathology. They are very common.
- Hyperplastic - most common, benign.
- Adenomatous - quite common, pre-malignant.
- Hamartomatous - rare, weird & wonderful.
- Inflammatory, AKA inflammatory pseudopolyps - associated with IBD.
Most common (images):
Inflammatory bowel disease
The bread 'n butter of gastroenterology. A detailed discussion of IBD is in the inflammatory bowel disease article. It comes in two main flavours (Crohn's disease, ulcerative colitis).
Features helpful for the diagnosis of IBD - as based on a study:
- Basal, i.e. crypt base, plasmacytosis with severe chronic inflammation,
- Crypt architectural abnormalities, and
- Distal Paneth cell metaplasia.
- Microscopic colitis may refer to a microscopic manifestation of an unspecified disease process that can be apparent macroscopically. This section links to a pair of diseases (lymphocytic colitis and collagenous colitis) that are considered to only have microscopic manifestations and characteristic clinical presentation.
- Abbreviated EC.
- This section covers non-specific colitides that appear to have an infective etiology.
- Diarrhea - typical symptom.
- +/-Erythema on endoscopy.
- Neutrophils predominant - key feature.
- The neutrophils are often superficial - they go to were the bad guys are.
- No architectural distortion - if acute.
- Inflammatory bowel disease - lymphoplasmacytic infiltrate predominant, usually has chronic changes.
- Ischemic colitis.
- Medications - focal neutrophils.
- Lymphocytic colitis - lymphocytes with a squiggly nucleus, may be confused with neutrophils.
- Specific causes of infective colitis - with a distinctive morphology.
Done if the patient is immunosuppressed, or there is clinical or morphological suspicion:
ASCENDING COLON, BIOPSY: - MILD ACTIVE COLITIS, SEE COMMENT. COMMENT: There is are no granulomas. The crypt architecture is normal. A benign lymphoid nodule is present. The differential diagnosis includes infective etiologies, early inflammatory bowel disease and ischemia. The histomorphology is more in keeping with an infective etiology as neutrophils are a predominant feature; however, clinical correlation is required.
- Abbreviated CMV colitis.
- AKA intestinal spirochetes; more specifically colonic spirochetes, colonic spirochetosis.
- May also be spelled amoebiasis.
- Usually in immune incompetent individuals, e.g. HIV/AIDS.
- Uniform spherical nodules 2-4 micrometres in diameter, typical location - GI tract brush border.
- Bluish staining of brush border key feature - low power.
Solitary rectal ulcer
- AKA solitary ulcer syndrome of the rectum, abbreviated SUS.
- AKA solitary rectal ulcer syndrome.
- Mucosal prolapse syndrome may be used as a synonym; however, it encompasses other entities.
These are very common. The are covered in a separate article entitled colorectal tumours.
- AKA carcinoid.
Goblet cell carcinoid
- Described in detail in the appendix article.
- AKA crypt cell carcinoma.
- Biphasic tumour; features of carcinoid tumour and adenocarcinoma.
- AKA melanosis coli.
Sodium polystyrene sulfonate
- AKA Kayexalate.
- Used to treat hyperkalemia - as may be seen in renal failure.
Graft-versus host disease
- Abbreviated as GVHD.
- Seen in the context of bone marrow transplants.
The histology of bowel transplant rejection is identical to GVHD - see GVHD.
- This section deals with chronic constipation that has no apparent cause.
General differential diagnosis for constipation:
- Adhesions - due to previous surgery.
- Congenital defect (Hirschsprung's disease).
- Medications/substance use.
- No changes.
- Colon within normal limits.
- Look for the Ganglion cells (submucosal plexus, myenteric plexus).
- Look for interstitial cells of Cajal (with CD117) - typically most common around the myenteric plexus.
- No significant vascular disease.
- No fibrosis.
- No loss of muscle.
Stains & IHC
- Routine H&E.
- Smooth muscle actin - confirm myocyte loss.
- Gomori trichrome - examine connective tissue.
- CD117 - to look for the interstitial cells of Cajal.
- <50% the expected = abnormal.
- Normal numbers not defined.
- <50% the expected = abnormal.
- HU - neuronal marker.
- A long list of things to report is contained the recommendation of a working group.
- Most pathology practises do not report much.
TERMINAL ILEUM, CECUM, COLON (ASCENDING, TRANSVERSE AND SIGMOID), COLECTOMY: - SMALL BOWEL, CECUM, AND COLON WITHIN NORMAL LIMITS. - FOUR LYMPH NODES NEGATIVE FOR MALIGNANCY ( 0 POSITIVE / 4 ). - NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY. COMMENT: Several stains were done: CD117: interstitial cells of Cajal present, no apparent decrease. SMA: no significant myocyte loss. Gomori trichrome: no abnormal fibrosis apparent. Tau: no abnormalities apparent.
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